How to Reasonably Control the Temperature of a Melting Furnace

After the prepared charge is loaded into the furnace, the temperature of the melting furnace should be strictly controlled. The purpose of controlling the melting furnace temperature mainly includes three aspects:

1. To meet the suitable first refining temperature requirements of various aluminum alloys.
2. To meet the suitable casting temperature requirements of various aluminum alloys.
3. To maintain a reasonable holding temperature so as to reduce oxidation loss on the surface of molten aluminum.

Before charging, the furnace chamber temperature must not be lower than 700°C.

According to production practice, the melting temperature of commonly used wrought aluminum alloys is usually controlled within the range of 50–100°C above the alloy liquidus temperature.

For aluminum alloys such as 3A21, 2A70, and 2A80, because they have a relatively strong tendency to form primary crystals of intermetallic compounds, the melting temperature is generally controlled at 720–760°C to ensure full dissolution of alloying elements.

For eutectic 4xxx series aluminum alloys, when silicon is added in the form of master alloy or crystalline silicon, the melting temperature should preferably be controlled at 750–780°C.

For other aluminum alloys, the temperature is generally controlled at 700–750°C.

In electrolytic aluminum plants, because the temperature of liquid primary aluminum is very high, solid return materials should first be used to reduce the temperature of the molten aluminum to the upper limit of the melting temperature. Then the alloying charge materials should be added.

After all charge materials have been loaded, the molten aluminum temperature should first be measured. When it is not lower than 750°C, the first refining should be carried out. When the furnace temperature drops to 730°C, slag removal should be performed.

During the second refining, the refining temperature should not be lower than 5°C above the upper limit of the casting temperature.

The casting temperature varies Depending on the product, the casting temperature for pure aluminum is 690~710°C. For aluminum alloys, the melting temperature during furnace cleaning is as high as 850°C. After heating for a certain time, the slag is allowed to soften before cleaning. During furnace drying, a wider temperature range is controlled, from 100°C to 980°C, with holding at different temperature points for a certain time. In resistance-heated mixing furnaces, since the heating elements are generally located above the surface of the molten aluminum, heat transfer mainly relies on radiation. The furnace temperature is usually the furnace chamber temperature, and the measured furnace chamber temperature varies depending on the thermocouple placement. In resistance-heated mixing furnaces, thermocouples are usually placed at the furnace top. The measured furnace chamber temperature is usually higher than the molten aluminum temperature. In production practice, the heating power should be determined according to specific circumstances and is usually variable. Lower power is used in resistance-heated mixing furnaces, while higher power is used when high temperatures or rapid heating are required. When maintaining heat, never use high-power heating; otherwise, the switching frequency of the power switch will be too fast, which may damage the electrical equipment.